6.(Engin.)The efficiency of an engine, especially a steam pumping engine, as measured by work done by a certain quantity of fuel; usually, the number of pounds of water lifted one foot by one bushel of coal (94 lbs. old standard), or by 1 cwt. (112 lbs., England, or 100 lbs., United States).

7.(Com.)Tax, toll, impost, or customs; excise; any sum of money required by government to be paid on the importation, exportation, or consumption of goods.&hand; An impost on land or other real estate, and on the stock of farmers, is not called a duty, but a direct tax. [U.S.]
Ad valorem duty, a duty which is graded according to the cost, or market value, of the article taxed. See Ad valorem. -- Specific duty, a duty of a specific sum assessed on an article without reference to its value or market. -- On duty, actually engaged in the performance of one's assigned task.